A new treatment option for breast cancer is the administration of tumor-targeted natural killer (NK) cells, specialized white blood cells, which have been genetically modified to specifically recognize and lyse cancer cells in vivo. Central aim of this project is to develop a non-invasive magnetic resonance (MR) imaging technique for monitoring the in vivo distribution, tumor accumulation and cytotoxicity of NK cells, which are directed against ErbB2-positive breast cancers. The imaging approach takes advantage of the well- documented physicochemical characteristics of particulate iron oxide nanoparticles, which can be incorporated into leukocytes and which can be depicted with MR imaging. The overall hypothesis is that NK-cells, labeled with clinically applicable iron oxide nanoparticles, can be traced non-invasively in vivo with MR imaging and that a tumor accumulation of the labeled cells can be proven with this imaging technique by significant tumor signal changes. Genetically engineered NK cells, directed against the ErbB2 antigen on breast cancer cells, will be labeled with iron oxide nanoparticles. Initial cell culture experiments will be carried out to prove, that the labeled NK cells can be depicted with clinical MR scanners and that the iron oxide label does not impair the cytotoxicity of the NK cells against breast cancer cells. Subsequent in vivo studies will be performed before and after intravenous injection of ErbB2-directed NK cells or non-directed control cells into athymic rats with implanted ErbB2-positive and ErbB2-negative human breast carcinomas. The in vivo distribution of the labeled NK cells will be monitored with MR imaging, using a 3T clinical MR scanner and T1-, T2- and T2*-weighted sequences. We hypothesize, that the tumor accumulation of the labeled NK-cells can be depicted by a significant decline in tumor signal intensity on these MR images. Conversely, a lack of signal changes of the tumor tissue after injection of labeled NK cells should be indicative of a lack of NK cell accumulation in the tumor tissue. Finally, the NK cell accumulation in the tumor tissue, as diagnosed by MR imaging on day 1 and 2 after NK cell administration, will be correlated with a subsequent NK-cell induced tumor cytotoxicity, as measured by an impaired tumor growth several days after NK cell administration. Complementary histopathologic and spectrometric studies, correlated with the MR findings, will examine the underlying NK cell tumor accumulation that influences the observed MR signal characteristics and potentially impaired tumor growth. Planned endpoints are (1) to establish a non-invasive MR imaging technique to monitor the accumulation of iron-oxide labeled, genetically engineered NK cells in ErbB2-positive breast cancers and (2) to detect the accumulation of labeled ErbB2 targeted NK cells in ErbB2 positive breast by a significant decline in tumor signal intensity on MR images. Since we use clinically applicable contrast agents and MR scanners, our imaging technique would be in principle readily accessible to patients. PUBLIC HEALTH RELEVANCE: The planned research project is designed to develop a non-invasive MR imaging technique for in vivo tracking of tumor-targeted natural killer cells (specialized white blood cells) to breast cancers. This imaging technique could help to correlate the presence and duration of natural killer cell accumulations in target tumors with the presence and extent of an expected natural-killer cell induced tumor growth inhibition. The information provided by this new MR imaging technique could be helpful for preclinical assessments of new tumor immunotherapies, for the design of translational clinical trials, and later, the assessment of those adoptive immunotherapies in clinical practice.